Iowa doesn't publish a death index, therefore, you have to look for other sources for this kind of info.
You can do a Google search for Lucas County Iowa Cemeteries and look for her in the inventoried cemeteries.
You can contact the Lucas County Genealogical Society, http://iagenweb.org/lucas/Resources/LCGS.htm
. You can ask if they have death info and will look up her obituary.
You can contact the Chariton Public Library, www.chariton.lib.ia.us/use-the-library/genealogy2
and ask them the same question. Successful Searching!